This invention relates to an automatic playing system for playing a tune on a keyboard musical instrument and, more particularly, to an automatic player appropriate for the keyboard musical instrument and a sensor incorporated in the automatic player for detecting motion of a plunger.
The automatic player includes a plurality of solenoid-operated key actuators, driver circuits and a controller. The solenoid-operated key actuators are provided under the black/white keys, and include respective solenoids, a yoke and respective plungers. The solenoid is a wire wound on a bobbin, and the wire is connected through the associated driver circuit to the controller. The solenoids are assembled with the yoke, and the associated driver circuits selectively energize the solenoids so as to produce magnetic fields. The plungers are inserted into the bobbins, and are projectable from and retractable into the solenoids. The yoke is mounted on a key bed, and the plungers are arranged in the lateral direction so as to be opposite to lower surfaces of the associated black/white keys.
The automatic player includes plural solenoid-operated key actuators, driver circuits and a controller. The solenoid-operated key actuators are provided under the black/white keys, and include respective solenoids, a yoke and respective plungers. The solenoid is a wire wound on a bobbin, and the wire is connected through the associated driver circuit to the controller. The solenoids are assembled with the yoke, and the associated driver circuits selectively energize the solenoids so as to produce magnetic fields. The plungers are inserted into the bobbins, and are projectable from and retractable into the solenoids. The yoke is mounted on a key bed, and the plungers are arranged in the lateral direction so as to be opposite to lower surfaces of the associated black/white keys.
While the automatic player is performing a tune, the controller selectively instructs the driver circuits to energize the associated solenoids with driving signals, and the energized solenoids cause the associated plungers to push the associated black/white keys, upwardly. The black/white keys are rotated without any fingering, and actuate the associated actions so as to drive the hammers for rotations toward the sets of strings. The hammers strike the associated sets of strings, and generate the piano tones along the tune.
If the magnitude of the driving signals is constant at all times, the associated black/white keys are pushed with constant force, and, accordingly, the hammers strikes the associated sets of strings at constant intensity. The sets of strings generate the piano tones at a constant loudness level, and make the tune flat. In order to vary the force exerted on the black/white keys depending upon the loudness level to be imparted to the piano tones, the driving circuits vary the magnitude of the driving signals through a feedback control. Position sensors or velocity sensors are provided in association with the plungers. The sensor associated with the plunger is hereinbelow referred to as xe2x80x9cplunger sensorxe2x80x9d. The controller checks the feedback signals from the plunger sensors to see whether or not the plungers are moved at target velocities. If the actual velocity is larger or smaller than the target velocity, the controller instructs the associated driver circuit to vary the magnitude of the driving signal. Thus, the plunger sensors are indispensable in the feedback control.
FIG. 1 shows a typical example of the plunger sensor incorporated in a prior art automatic player. Reference numerals 1 and 2 designate the plunger and the solenoid, respectively. The plunger 1 passes through the solenoid 2, and projects from both ends of the solenoid 2. The plunger sensor is implemented by the combination of a gray scale 3 and a photo-interrupter 4. The gray scale 3 is attached to the lower end portion of the plunger 1, and is movable together with the plunger 1. The gray scale 3 is a transparent plate coated with an achromatic color layer. The achromatic color layer is varied in lightness in the direction of the center axis of the plunger 1.
The photo-interrupter 4 is stationary with respect to the solenoid 2, and has a light emitting element and a light detecting element. The light emitting element is opposed to the light detecting element through the gray scale. The light emitting element radiates a light beam toward the gray scale, and the achromatic color layer transmits part of the light beam to the light detecting element. The amount of the incident light on the light detecting element is varied together with the lightness of the achromatic color layer. When the plunger 1 is moved with respect to the solenoid 2, the light beam passes the achromatic color layer at a certain point different from the previous point, and the amount of the incident light is varied. The light detecting element produces the feedback signal representative of the amount of the incident light, and the controller determines the current plunger position on the basis of the feedback signal. The quotient between the length and the lapse of time represents the plunger velocity.
Another prior art plunger sensor directly detects the plunger velocity. The plunger sensor is implemented by the combination of a magnet and a coil. The magnet is attached to the lower end portion of the plunger, and is inserted into the hollow space inside of the coil. The magnet is movable together with the plunger, and the coil is stationary with respect to the solenoid. When the solenoid is energized, the plunger is moved together with the magnet, and the magnet gives rise to electric current flowing the coil. The electromagnetic induction takes place, and the electromotive force is indicative of the velocity of the magnet and, accordingly, the velocity of the plunger.
A problem is encountered in the prior art plunger sensor shown in FIG. 1 in that the manufacturer can not make the solenoid-operated key actuator compact. This is because of the fact that the manufacturer is not permitted to reduce the length of the gray scale 3 below the plunger stroke to be monitored. If the gray scale 3 is shorter than the plunger stroke, the controller can not determine the current position over the monitored range on the basis of the feedback signal. Moreover, the gray scale 3 is to be prolonged in the direction of the plunger stroke, because the manufacturer is to vary the lightness on the achromatic color layer in the direction of the plunger stroke. Thus, the manufacturer can not reduce the prior art solenoid-operated key actuator to a length shorter than the total length of the solenoid 2 and the plunger stroke. The gap between the black/white keys and the key bed is so short that the prior art solenoid-operated key actuators assembled with the plunger sensors are hardly installed in a small-sized acoustic piano. Even though the automatic player is to be installed in a large-sized acoustic piano, the gap between the black/white keys and the key bed sets a limit on the total length of the prior art solenoid-operated key actuators, and the manufacturer can not sufficiently lengthen the solenoid 2. This means that the prior art solenoid-operated key actuators can not exert large force on the black/white keys.
Another problem inherent in the prior art plunger sensor is aged deterioration. The gray scale 3 is not directly connected to the photo-interrupter 4. The gray scale 3 and the photo-interrupter 4 are independently connected to the plunger 1 and another stationary part. The relative relation is liable to be varied during a long time period. When the relative relation is varied from the initial state, the feedback signal does not exactly represent the current plunger position, and the controller can not adjust the force exerted on the black/white key to a target value.
Yet another problem inherent in the prior art plunger sensor is it fails to exactly control the plunger due to noise contained in the feedback signal. The gray scale is varied in the lightness in the direction of the plunger motion, and the ratio between black and white is successively changed on the transparent plate for the lightness. When the light beam is transmitted through the gray scale, a ripple tends to take place in the feedback signal. The controller determines the plunger velocity through the differentiation. However, when the controller differentiates the feedback signal, the ripple causes noise, and the controller fails to exactly grasp the current plunger velocity due to the noise. This results in the failure to move the plunger along the target trajectory.
The prior art plunger sensor of the type having the magnet and the coil has a problem in a small signal-to-noise ratio. While the plunger is moving at a low speed, the electromotive force is small, and the feedback signal is not reliable due to the small signal-to-noise ratio. It is difficult to determine the dead point of the plunger on the basis of the feedback signal from the prior art plunger sensor. It is necessary to form the coil not shorter than the plunger stroke. This results in that the plunger is to downwardly project from the solenoid by the length as long as the plunger stroke. Thus, another problem encountered in the second prior art plunger sensor is same as the first problem inherent in the first prior art plunger sensor shown in FIG. 1.
It is therefore an important object of the present invention to provide an automatic player, which is installable in a small-sized keyboard musical instrument.
It is also an important object of the present invention to provide a plunger sensor, which is compact and reliable regardless of the plunger speed.
In accordance with one aspect of the present invention, there is provided an automatic player incorporated in a musical instrument for playing a tune on an array of manipulators without a human player comprising solenoid-operated actuators including solenoids respectively creating magnetic fields while driving signals are flowing therethrough and plungers respectively associated with the manipulators of the array and respectively projecting from the solenoids along trajectories for pushing the manipulators, respectively, when the associated solenoids create the magnetic fields, plunger sensors for producing detecting signals respectively representative of current positions of the plungers on the trajectories, each of the plunger sensors including a reflecting means attached to one of the associated plunger and a member stationary with respect to the associated solenoid and a photo-coupler attached to the other of the associated plunger and the member and radiating a light beam toward the reflecting means for producing one of the detecting signals from a reflection returning from the reflecting means, and a controlling system connected to the solenoids and the photo-couplers, determining a magnitude of the driving signals on the basis of the current positions and supplying the driving signals to the solenoids, respectively.
In accordance with another aspect of the present invention, there is provided a plunger sensor associated with a solenoid-operated actuator comprising a reflecting means attached to one of a plunger of the solenoid-operated actuator and a member stationary with respect to a solenoid of the solenoid-operated actuator, and a photo-coupler attached to the other of the plunger and the member and radiating a light beam toward the reflecting means for producing a signal representative of a current plunger position on a trajectory from a reflection returning from the reflecting means.